Method of producing light refracting optical elements having aspherically curved optical interfaces



Aug. 10, 1954 'n E ET AL 2,685,821

METHOD OF PRODUCING LIGHT REFRACTING OPTICAL ELEMENTS HAVINGASPHERICALLY CURVED OPTICAL INTERFACES 6 Sheets-Sheet 2 Original FiledJune 27. 1947 INVENTORS EDGAR o. TlLLYER ALVA BENNETT TORNEYS Aug. 10,1954 E. D. TILLYER ET L 2,535,821

METHOD OF PRODUCING LIGHT REFRACTING OPTICAL ELEMENTS HAVINGASPHERICALLY CURVED OPTICAL INTERFACES Original Filed June 27, 1947 6Sheets-Sheet 5 ASPHERIC SURFACE 0.5 X= 0.000(3001996Y +0.0oo oo09zl9QYo.ooooooooo'13|5Y Y \o 2.0 30 4o 45 50 GLASSES 29 N LGI'I 955.0

30 N L6H \758.8

Aug. 10, 1954 E. D. TILLYER ET AL 2,685,821

METHOD OF PRODUCING LIGHT REFRACTING OPTICAL ELEMENTS HAVINGASPHERICALLY CURVED OPTICAL INTERFACES Original Filed June 27, 1947 6Sheets-Sheet 6 o Q INVENTORS EDGAR unuxek LL ALVA FLBENNETT J %&

Patented Aug. 10, 1954 UNITED STATEg PATENT GFFICE METHOD OF PRQDUCINGLIGHT REFRACT- ING OPTISAL ELEMENTS HAVING AS- PHERICALLY CURVE!)OPTICAL INTER- FACES Edgar D. "llillyer, Southbridge, Mass, and Alva. H.

Bennett, New Canaan,

Company,

American ()ptical assignors to Southbridge,

Conn,

Mass, a voluntary association of Massachusetts 3 Claims. 1

The present invention relates to objectives of which typical examplesare lens systems used as objectives in the photographic field forproducing an image either on a film (as in a camera) or on a screen (asin a projector), and lens systems used as microscope objectives andtelescope objectives. This application is a division of copendingapplication Serial Number 757,348 which was filed June 27, 1947, andwhich issued May 13, 1952, as Patent No. 2,596,799.

In working out high quality objectives of this character, the designeroccasionally a system where the field is good due to good reduction ofdistortion, coma, astigmatism and curvature, and good conditions ofaxial and lateral color, but where the system would in general bediscarded because of excessive spherical aberration or excessivevariation in spherical aberration with color. There are other systemswhose commercial value is reduced because spherical aberration orvariation in spherical aberration with color imposes a reduced apertureratio on the system. it is an ob- J'ect of the present invention toovercome the defects in such systems while preserving their good fieldcharacteristics by including in the lens system aspheric surface whoseaccuracy may be kept within desirable close limits practical methods ofmanufacture. Such an aspheric surface, in accordance with our invention,may be on a member already a part of the system or on a member purposelyadded thereto.

Asphe' ic surfaces have been generally avoided in lens design because ofthe difilcultles involved in obtaining accuracy in manufacture and therelative high cost of producing an aspheric surface as compared to aspherical surface which can be generated according to standardprocedure. In accordance with our invention the accuracy with which theaspheric surface produced conforms to the curvature laid out by thedesigner is rendered substantially less critical by forming the asphericsurface internally within a member. This results in causing the changein refractive index in passing through the aspheric surface to besubstantially less than in the usual design where the aspheric surfaceis an external surface. Further economies may be effected where this isdesirable by causing a lamination of two or more layers of glass tosoften under heat and 2 sink into conformity with the predeterminedcurvature of an underlying surface, thereby creating the desiredaspheric curvature of the interface or interfaces between the layers ofglass.

In the drawings which illustrate our invention I shows a simple cameralens system corrected in accordance with our invention;

Fig. II shows an achromatic microscope objective similarly corrected,together with its specifications;

Fig. III is a vertical sectional view through a heating chamber in whichour corrector member is being shaped, the chamber being showndiagrammatically;

Fig. IIIA is a sectional View through the glass lamination after it hasbeen dropped in the heating chamber of Fig. III and indicating thefurther grinding and polishing operations which are to be performedthereon;

Fig. IV is a graph illustrating the improvement in longitudinalspherical aberration brought about by the use of our corrector member inthe microscope objective of Fig II;

Fig. V shows a projection objective of the Cooke triplet type togetherwith its specifications;

Fig. VI shows the same projection objective provided with a correctorplate in accordance with our invention;

Fig. VII shows the same projection objective with a triplet correctorplate;

Fig. VIII shows the same projection objective with two doublet correctorplates;

Fig. IX shows the same projection objective with a still furthercorrector plate embodying our invention;

X is a graph comparing the spherical aberration occurring in theobjective systems shown in Figs. V and VI; and

Fig. XI is a graph showing the aberration occurring in the objectivesystems of Figs. VII, VIII and IX respectively.

As an example of how the invention may be applied, We will firstconsider a simple camera lens system such as the fixed focus, handcamera objective of the double meniscus type illustrated in Fig. I. Thesimple system consists of the usual two l nses for power, uncorrectedfor color, and desi nated respectively 5 and S in the drawl-ng. Thissystem has very pronounced spherical aberration.

Into this system is now introduced, in accordance with our invention, acrown-flint meniscus 8, l of substantially no power, the meniscus E, 1preferably being positioned near the stop of the system. W e may makethe member 6, l in various ways. For instance, the flint element 6 maybe ground with an aspheric surface 6a complemental to the surface 1a ofthe crown element F, and the two elements cemented together using acement of approximately the same refractive index as that of the crownglass, or that of the fiint glass or a refractive index intermediate thetwo. We prefer, however, to fuse together two flat plates of glasseswhich lend themselves to fusing together. These two plates, united intoan integral member, are dropped by means of heat on to a refractorymaterial so that the interface assumes the desired aspherical curve;then the two outer faces of the member are ground and polished to aspherical curve or piano by the usual means. These spherical or planecurves may be such as to give the member little residual power or themember may have specially designed external surfaces so that it becomesa part of the refracting system.

The art of fusing two glasses together has been well developed in theophthalmic lens industry in the manufacture of bifocal lenses; andtherefore there are available a considerable variety of glasses whichadapt themselves to fusing. For instance, glasses of the followingoptical constants may be obtained from glass manufacturers such asPittsburgh Plate Glass Co. and will fuse together:

There are a variety of glasses which when properly selected in pairswill fuse together successfully.

From this it will be seen that either a considerable or a relativelyslight diiference in refractive indices is available, and this is truealso as to reciprocal relative dispersion, each of these two valuesbeing termed in this specification an optical constant of the respectiveglass.

The designing of an optical system with good reduction of the variousaberrations including coma is essentially the computation of opticalpath lengths of various rays passing through the system, the opticalpath length for each ray being expressed by the formula n l E Z=constant to A Z 4 where m is index of rth medium Zr is length in rthmedium n is number of elemental paths The actual computing of theoptical path lengths of the various rays may be done in various knownways. One excellent way is described by Dr. A. Estelle Glancy in anarticle On the theory and computation of an aspheric surface in theJournal of the Optical Society of America, vol. 36, No. 7, July 1946,pages 416 to 423 inclusive. As the actual computation of a specificsystem forms no part of the present invention. the work done by Dr.Glancy in computing given lens systems is not reproduced here.

It is of interest however to use Dr. Glancys computations to giveconcrete dimensions to the simple objective shown in Fig. I. Assumingthe following values for the surfaces of this objective with allsurfaces spherical she computed a system with the interface betweenelements 6 and 7 aspheric, the aspherical curve being as follows:

[Aspherical curve, osculai-ing radius, 88.00 mm.]

l l Departure Semidlameter Excavation I l 1 radius 88 l Mm. Mm. Mm. l 00 0 l 5. 154 0. 1725 0. 0214 7. 292 0. 3901 0. 0875 s. 931 0. 6547 o.2002 10. 309 0. 9681 0. 3m l 11.518 I 1.3342 0. 57st l The followingtables afford a comparison of the spherical aberration present in thefirst system with all surfaces spherical, with the spherical aberrationpresent in the second system with an aspheric surface:

Spherical syslem Sphcrical (KI/13): aberration Mm Mm 0 i 1/5 2. 581 0.ll 2/5 5. 177 0. 22 3/5 7. 783 -0. 33 4/5 l0. 407 -0. 44 5/5 l3. 050 0.52

Asphefical system Spherical (Kl/l3) aberration Coma Mm. Mm

where Kl is the aperture for the particular ray,

accuses 5 and lsisthe -Klforfullsemi-aperture ofthelens system.

It is importantto analyze these values to determine what increase inspherical aberration occurs" when in actual production the asphericsurface. does not accurately conform to the computed' curve. Thediiferenc'e in refractiveindices between the dense flint glass ofelement 6 and the crown glass '5" is 1..62891.5292=0.0997. If, thesurface actually: obtained departs from the theoretic surface. by. 0.0lmm. the difierence in optic'a-lpath, which is the=determining factor,isLonlY 0.000997 mm. or about one-tenth of the error in surfacing thelens element.

T-ha-t th'ere should be such a minimizingof the effect of a deviation ofthe aspherica'l surface from thetheoretical curve, has an importantbearing on the 7 cost ofproduci'ng these aspherical surfaces. Assumingthat the surfaces to and la areproduced hy'grinding and-polishing, theconventional design omens-systemwith-theaspheric surface an externalsurf'ace entails long and tedious work on the part of the operator toobtain the requisite-accuracy of'curvature. With a design oflens systemaccording to our invention, with an internal aspheric surface forcompensatingforspherical aberrationor for v riation' in sphericalaberration with color, much less care and precision need'be'eXercised-ingrinding and polishing the aspheric surfaces such as the surfaces 6a"and la, particularly where a cement is used which is eif'ectively acontinuation of the lens 6 or the lens 1 because the index of refractionof'the cement is approximately the same as that. of the "lensli or thelong i or where the index ofirefractionof the cement is intermediatethat of the two lenses;

It is preferable, as indicated above, to produce the aspheric surfaces;by fusing together two sheets of the proper glasses and. then. drop thelaminated. glass article'by heating. it while supported on a refractorysupport having surface curvatures so controlled asto produce an interface 6a; la of the desired? contour. A heating furnace s for this urposeis conventionally illus trated in Fig. III; the laminatedcorrectormember made upoftwo or moresheets of 'glass fused togetherbeing placed on a refractory support 5 iii It has been'found that theflow or deformation of'the glass (when softened by heat)- is onlypartially in a direction to bring it into contact with the supportingrefractory. To some extent there is a sidewise flow of the glass,particularly in the vicinity of high points of the supporting'efi'actory. This causes the surfacecurvatures inthe vicinity of thesehigh points to be slightly flatter than the theoretical curvature. Inorder to improve the accuracy obtainable in the final product; thedeparture in contour of the interface of the corrector' member(heat-softened; and dropped into contact with the refractory) isdeterminedand then the shape of the surface of the supporting refractoryis altered by a compensating amount. This is accomplishedv by buildingup. or reducing different. portions of thecurved supporting surface oftherefractory by amounts sufiicient to compensate for the variationsvexperimentally dete'niined. This may requi e the dropping of several;different curves and. several diiferentalterings of the supporting.surface'of the refractory.

The nature of therefractory material itself is important; The preferredrefractory must not stick to the glassduring'tlie' heating and coolingoperation: Moreover it should be: a composition: having little or notendency to change in shape;

or become distorted as to supporting surface shape during the actual.dropping process. A composition for producing a material having theabove desirable characteristics and as disclosed in copendingapplication of. Edgar D. Til1yer,.

Serial No.485g843, filed May 6, 1943, and issued September. 20., 1.9.49,as Patent No. 2,482,698; is substantially as follows:

Much difiiculty, has been encountered in the dropping of: glass articleson refractories to produce controlled surface" curvatures because duringthe time that the glass is soft and in a condition' to change its shapethe supporting refractory surface is itself distorted due tothe'elevat'ed temperatures at which the dropping process is carried on.It is important, therefore, to control the composition of the refractorymaterial so as to avoid the tendency to become distorted during thedropping process, or to shrink an additional"amount-with each successiveuse.

When the. laminated corrector member has thus been molded'by dropping,it will have some; whatthe configuration shown in full lines in Fig-III-Ahflv the drawings. The exterior surfaces 65 andlli are ground. awayto the desired curvatures, for instance. the curvatures indicated indash lines. (it and. To. in.- Fi'g. IIIA, and are. then polished, piano.being considered acurvature as the termis-thus broadly used. In someinstances, both exterior surfaces may have substantially no power, thecorrector member being merely an addition to. alens-s-ystem with thepower in the other elements of such system. This is the situationin thesimple camera lens system above described. In other: instances, one orboth exterior surfaces may be' ground and polished to have poweiv. Herethe aspheric surface is, in eifect, inserted: within one of the lenselements of the. optic system.

Since the sheets of glass have been fused, no error is introduced byadhesive interposed between thextwo gl'asses. Excellent results areobtainab'le; therefore; in correcting for spherical aberration: and forvariation in spherical aberration with color by producing an asphericsurface by a process which due to the use of a molding techniqueiseconomical and capable producing large quantiti s without excessivelabor cost;

Ehe. invention will now b'e'discussed in con nection with: examples. ofmor complicated lens systems which have been designed in accordance withour invention;

The achromatic microscope objective ofFig. II is of conventional designincluding two doublets, the-first doublet being'niade up of the negativeflint element ll and the positive crown element i2, while the seconddoublet ismao'ie up of the negative flint element ES and the positivecrown element" it; Both doublets are cemented. By

use oft'wo' doublets in this manner, chromatic aberration may besubstantially reduced; andtheobjectiveas illustrated hasbeen' designedto conect'forcolbras'well" as for coma and astigmatism. A specificationfor this objective is as follows:

Lenses ND V Radii spacings Rz=+ 5. 32 12 1. 5125 60. 5 tz= 1. 52

81 17. 01 R4=+1638. 13 1. 617 38. 5 ta 2. 18

R5= 10. 9O 14 1. 5125 60. 5 t4= 2.03

Aspheric 16 1. 57241 57. 4

wherein R1 to Rs are the radii of the spherical surfaces on the lenselements I to VI of the system, except as otherwise noted, the plus andminus signs refer respectively to surfaces convex and concave to thefront, in to t; are the thicknesses of the elements, 31 and s2 are theair space distances between adjacent elements, ND is the refractiveindex with respect to the D line of the spectrum, and V is thereciprocal relative dispersion of the elements. The longitudinalspherical aberration for this particular system is shown by the curve Aat the left of Fig. IV. A corrector member may be added to the lenssystem as shown in Fig. 2 to substantially reduce this sphericalaberration, two elements I and It with an interface Ilia, 5a beingprovided for this purpose. The interface is an aspheric surface whoseformula has been computed by the expansion of the aberrations into apower series, and determining the necessary aspheric surface for theircorrection. The resulting formula for the aspheric surface is:

X= 0.00000121475 fi -01100734423 y 0.0Gfi032546 1 in which y is thedistance from the axis of the optical system and a: is the departure ofthe aspheric surface from piano.

While a light flint glass has been used for element !5 and a bariumcrown glass has been used for element i5, the indices have a differenceof 1.57e51.5v24=o.00v1. Since as explained above it is the difference inoptical path which is the determining factor in designing the asphericsurface l5a, ifia, the difference in refractive indices of only 0.0071affords considerable tolerance in the accuracy of this aspheric surface.The particular glasses specified in this design for the elements It andit are not of the readily fusible type and therefore it is preferable togrind and polish the aspheric surfaces for the interface [5a, lBa andcement the surfaces together with an adhesive having a refractive indexof approximately 1.57 to 1.58.

With a corrector plate of this design the longitudinal sphericalaberration of the microscope objective of Fig. II is so nearlyeliminated as to give the curve B shown in the graph at the right ofFig, IV.

In Fig. V is illustrated a typical projection objective of the Cooketriplet type. This design of objective has good field characteristics,and as is conventional in Cooke triplets comprises a positive lens 18, asecond positive lens 25 spaced therefrom with a negative lens 18interposed therebetween. The specifications of the particular tripletwhich we have selected as an example are set forth in Fig. V and are asfollows:

Lenses N V Rcdii spacings 20 (III) 1. 5161 64. 4

wherein R9 to R14. are the radii of the spherical surfaces on the lenselements I to III of the system, the plus and minus signs referrespectively to surfaces convex and concave to the front, ii to is arethe thicknesses of the elements, s1 and 52 are the air spac distancesbetween adjacent elements, ND is the refractive index with respect tothe D line of the spectrum, and V is the reciprocal relative dispersionof the elements.

Figs. VI, VII, VIII and IX show various designs embodying one or morecorrector plates for reducing the spherical aberration of the system andthe variation in spherical aberration with color. The corrector plateshown in Fig. VI is made up of two plates of glass 22 and 23 having therefractive indices respectively 1.5795 and 1.57241. The glass 22 has areciprocal relative dispersion 41.0 and that of glass 23 is 57.4. Thesetwo glasses ma be either cemented or fused together. The surfaces R15and R17 are plane and the formula and the data for the aspheric surfaceRm which has been computed to reduced aberration in the objective systemof Fig. V is given in Fig. VI and are as follows:

[Asphcric Surface Sa=0.5]

X=+0.000000105 y +0.00000078309 y0.0000000006256 y" and in Fig. X is acomparison of the longitudinal spherical aberration of this objectivewhen uncorrected and when corrected, the group of curves at the left ofFig. X showing the aberration of the objective without a corrector plateand the group of curves at the right of Fig, X showing the sphericalaberration when using the corrector plate of Fig. VI. The sphericalaberration for the D line of the spectrum is indicated in each of thetwo groups by the curve marked D and Do, the spherical aberration forthe C line of the spectrum by the curve marked C and Co, and thespherical aberration for the F line of the spectrum by the curve markedF and F0 respectively. The difference between the two V values (see Fig.VI) which are 41 and 57.4 respectively has been purposely chosen so asto control the variation in spherical aberration with color as indicatedat the right of Fig. X.

Another solution of the problem of correcting the objective of Fig. Vfor spherical aberration is shown in Fig. VII, a triplet correctormember being used. This triplet corrector member is made up of thedoublet corrector plate of Fig. VI together with an additional internalaspheric surface R18 afforded by an additional glass 25 having an indexof refraction 1.5725 and a reciprocal relative dispersion 42.5. The rearsurface R19 is piano. The three glasses may be either cemented or fusedtogether. The formula aesaeai 9 and the .data :for :additional :aspheric.sur- -face are'given .inll-ig. VII and are as follows:

[Additional nspheric Surface The resultant improvement in thelongitudinal spherical aberration is shown at ithBllGf-t of :Eig. XI.Here there areithree V values, :namely, 4 57.4 and 42 .5. :In XI where.the spherical aberrations for the three specified :lines .of thespectrum are indicated by the .iletter ET, Cr andFrrespectivelyit.willm'notedsthat theichoiceof 7 :these three V'valuesih'asxresultediin axsti'll turther iimprovernent inithe control:of variation inzsphenical aberration with :color.

In Fig. is .illustratedstill another :solution of the problem ofcorrecting ith'e Cooke triplet -of and the resulting correction-in thelongitudinal 'sphericalaberrationis shown in thecentralgroup of 'curvesD,"C and F ot Fig.

In Fig. IX is illustrated a still further solution or the problem ofcorrecting the spherical "aberration "of the Cooke triplet "of Fig. V.Here a doublet Corrector plate is used"ma deup of the glasses 29 and 3!having the refractive indices respectively 1161"? and l .6 T1. Thereciprocal "relative dispersion of the glass 29 is 55:0 and that ofglass '3'fi is 518:8. 'The formula and the data for the aspheric surfaceR23 '01? this Corrector plate are shown in Fig. IX and are as follows:

[Aspher m Surface 52:0.5]

.X='0.Okl(10001936'wi l);00000692199;y +0LE0000'flG0O73l5511 and theresulting correctiontin the longitudinal spherical aberration of thetriplet of Fig. V is :shown by curves 133, Cs and at the right of Fig.XI.

The examples We have given in Figs. V, VI, VII and VIII all show tovarying degrees a re- 'duction in the variation in spherical aberrationwith color, :as well .as a reduction .in spherical aberration. .If theproblem should be tocorrect an objective with excellent sphericalaberration correction for the D line but bad variation of the sphericalaberrationnwi-th color, we would accordance with our inventionselect aplurality of glasses having nearly the same index of re fraction for theD line but with different relative dispersions to form the correctormember. An example of a .pair of glasses suitable .for correcting thevariation in spherical aberration .1 0 with .color under suchcircumstances is Barium Crown with an index .of refraction 1.616 and a Vvalue 49combined with ordinary flint having an index of refraction 1.616and a V value 36.

If 'it is desired to change the spherical aberration alone and leave thevariation of spherical aberration with color the same as before, apairof glasses should he used having approximately the same V value but withdifferent indices of refraction. lhis latter is rarely desired.

.In all of the examples just discussed it will be noted that to improvean objective which has excessive aberration of one 'kind or the other, aselection is made of glasses having appropriate differencethere'be'tweenin an optical constant. If the objective is defective because ofspherical aberration, the glasses are selected with regard to thedifference in the optical constant, index of refraction. If theobjective is defective because of variation in spherical aberration withcolor, the glasses are selected with regard to the difference in theoptical constant, reciprocal relative dispersion. Generally, theselection is made with regard to both of these optical constants.

.In these various embodiments of our invention the aspheric surface is asurface between lass elements attached to each other to form 'a unitwith an internal correcting surface. "Instead of a single 'aspheri'csurface a plurality of aspheric surfaces may be employed. The asphericsurface or surfaces is preferably placed at the so-called stop point.Being so positioned, "the oblique and axialbundles of rays go throughthe same portion of the .correcter member.

Our invention has wide application as it may be used to improve lenssystems of various olesigns where'the spherical "aberrations or thevariation "in spherical aberration with color is troublesome. Since thedesigner is thereby enable'd' toben'd his efforts first toward theimprovement of the field of the lens system by correction of coma,astigmatism, etc it affords him considerably greater latitude in thedesign of "his system. The correction for spherical aberration orvariation in spherical aberration or both can then-"be taken care of bymeans of our invention.

Our improvement ha the further distinct advantage that the apertureratio of the system is substantially improved by the correction madepossible by our invention, thereby substantially increasing thecommercial value of the optical system to which the invention has beenapplied.

While certain illustrative embodiments of our invention have shown anddescribed. it will be understood that our invention maybe otherwiseembodied and practiced within the scope of the following claims.

Having described our invention we claim:

1. The method of producing a light refracting optical'component havingan aspherically curved optical interface, for use in corr sting at leastone of the spherical and chromatic aberrations of a lens systemotherwise well corrected for distortion, coma, astigmatism and curvatureof field when said optical interface is located substan tially atthe-stop point in said'system, said-method comprising fusing a pluralityof substantially parallel-sided optically finished pieces of glasstogether in face-tdface relation so as to form a single integrallaminated member having an optical interface, each of said pieces ofglass having predetermined refractive dispersive optical constants andeach piece of glass differing appreciably from an adjacent piece ofglass in at least one of said optical constants, forming a supportingmember of refractory material of a type which may be readily altered inshape when desired by adding like refractory material thereto and byremoving material therefrom, said refractory material also being of atype to which glass will not adhere and which will not alter its shapeappreciably when heated to a temperature suincient to soften fordropping purposes glasses of the types provided said laminated member,forming on the upper surface of said refractory material a contour ofpredetermined curvature, said predetermined curvature of said uppersurface being aspherically shaped so as to closely approximate thepredetermined interface curvature for said system in accordance with thespherical and chromatic aberrations of said system to be corrected,placing said laminated member upon said upper surface of said supportingmember while said upper surface is maintained in a generally horizontalposition, raising the temperature of said laminated member to thesoftening temperature of the glasses of said laminated member andmaintaining said temperature only for a time sufficient to cause saidlaminated member to flow laterally and move downwardly into intimatecontact with said upper surface of predetermined curvature, therebycausing said laminated member to give to said optical interface anaspheric curvature for use in controlling at least one of said sphericaland chromatic aberrations, grinding and polishing the exposed surfacesof said laminated member at opposite sides of said optical interface toproduce refractive surfaces of known shapes thereon opticaliy alignedwith said optical interface, so that the departure of the asphericalcurvature of said optical interface from said predetermined asphericalcurvature desired for said system may be measured, and so that thenecessary compensating curvature for the upper surface of saidsupporting member may be determined, altering the refractory materialforming the contour of said upper surface so as to compensate for saiddeparture, and repeating said fusing, heating, grinding, polishing andaltering steps until an optical component having said desiredaspherically curved interface is obtained, whereby a large number ofsimilar optical com ponents each having the desired aspheric interfacemay thereafter be easily and economically produced by repeated use ofsaid supporting member.

2. The method of producing a light refracting optical component havingan aspherically curved optical interface, for use in correcting thespherical aberrations of a lens system otherwise well corrected fordistortion, coma, astigmatism and curvature of field when said opticalinterface is located substantially at the stop point in said system,said method comprising fusing aplural- 12 type to which glass will notadhere and which will not alter its shape appreciably when heated to atemperature sufiicient to soften for dropping purposes glasses of thetypes provided said laminated member, forming on the upper surface ofsaid refractory material a contour of predetermined curvature, saidpredetermined curvature of said upper surface being aspherically shapedso as to closely approximate the predetermined interface curvature forsaid system in accordance with the spherical aberrations of said systemto be corrected, placing said laminated member upon said upper surfaceof said supporting member while said upper surface is maintained in agenerally horizontal position, raising the temperature of said laminatedmember to the softening temperature of the glasses of said laminatedmember and maintaining said temperature only for a time sufficient tocause said laminated member to flow laterally and move downwardly intointimate contact with said upper surface of predetermined curvature,thereby causing said laminated member to give to said optical interfacean aspheric curvature for use in controlling spherical aberrations,grinding and polishing the exposed surfaces of said laminated member atopposite sides of said optical interface to produce refractive surfacesof known shapes thereon optically aligned with said optical interface,so that the departure of the aspherical curvature of said opticalinterface from said predetermined aspherical curvature desired for saidsystem may be measured, and so that the necessary compencating curvaturefor the upper surface of said supporting member may be determined,altering the refractory material forming the contour of saiduppersurface so as to compensate for said departure, and repeating saidfusing, heating,

grinding, polishing and altering steps until an optical component havingsaid desired aspherically curved interface is obtained, whereby a largenumber of similar optical components each having the desired asphericinterface may thereafter be easily and economically produced by repeateduse of said supporting member.

3. The method of producing a light refracting optical component havingan aspherically curved optical interface, for use in correcting thechromatic aberrations of a lens system otherwise well corrected fordistortion, coma, astigmatism and curvature of field when said opticalinterface is located substantially at the stop point in said system,said method comprising fusing a plurality of substantiallyparallel-sided optically finished pieces of glass together inface-to-face relation so as to form a single integral laminated member'having. an optical interface, said pieces of glass having predeterminedrefractive indices and predetermined dispersive indices, one of saidpieces of glass differing appreciably from an adjacent piece of glass indispersive indices while the refractive indices thereof are nearlyalike,

' forming a supporting member of refractory mapieces of glass differingappreciably from an adjacent piece of glass in refractive indices whileterial of a type which may be readily altered in shape when desired byadding like refractory material thereto and by removing materialtherefrom, said refractory material also being of a type to which glasswill not adhere and which will not alter its shape appreciably whenheated to a temperature sufiicient to soften for dropping purposesglasses of the types provided said laminated member, forming on theupper surface of said refractory material a contour of predeterminedcurvature, said predetermined curvature of said upper surface beingaspherically shaped so as to closely approximate the predeterminedinterface curvature for said system in accordance with the chromaticaberrations of said system to be corrected, placing said laminatedmember upon said upper surface of said supporting member While saidupper surface is maintained in a generally horizontal position, raisingthe temperature of said laminated member to the softening temperature ofthe glasses of said laminated member and maintaining said temperatureonly for a time suificient to cause said laminated member to flowlaterally and move downwardly into intimate contact with said uppersurface of predetermined curvature, thereby causing said laminatedmember to give to said optical interface an aspheric curvature for usein controlling said chromatic arberrations, grinding and polishing theexposed surfaces of said laminated member at opposite sides of saidoptical interface to produce refractive surfaces of known shapes thereonoptically aligned with said optical interface, so that the departure ofthe aspherical curvature of said optical interface from saidpredetermined aspherical curvature desired for said system may bemeasured, and so that the necessary compensating curvature for the uppersurface of said supporting member may be determined, altering therefractory material forming the contour of said upper surface so as tocompensate for said departure, and repeating said fusing, heating,grinding, polishing and altering steps until an optical component havingsaid desired aspherically curved interface is obtained, whereby a largenumber of similar optical components each having the desired asphericinterface may thereafter be easily and economically produced by repeateduse of said supporting member.

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